A method for producing SOI wafers by separating ions-implanted wafers after bonding, i.e., the ion implantation separation method (an art also referred to as the Smart Cut method (registered trademark)), has attracted attention as a method for producing SOI wafers, particularly SOI wafers each having a thin layer that enable the performance improvements of advanced integrated circuits.
The ion implantation separation method is an art (See Patent Document 1) to form an SOI wafer in the following manner: an oxide film is formed on at least one of two silicon wafers, and gas ions, such as hydrogen ions or rare gas ions, are implanted from a front surface of one of the silicon wafers (a bond wafer) to form a layer of the implanted ions (also referred to as a micro bubble layer or an enclosed layer) in the interior of the wafer. The oxide film is then interposed between the surface from which the ions are implanted and the other silicon wafer (a base wafer) so that these have close contact, and a heat treatment (a separation heat treatment) is then performed to cleave one of the wafers (the bond wafer) along the micro bubble layer so that the bond wafer is separated into a thin film. A heat treatment (a bonding heat treatment) is then performed to strengthen a bond between the wafers. At this point, the cleave surface (the separation surface) is a surface of an SOI layer and an SOI wafer having a thin SOI film with high uniformity is relatively readily obtained.
This ion implantation separation method is used not only to produce a bonded SOI wafer through an insulator film but also to produce a bonded wafer by directly bonding two wafers.
In the ion implantation separation method, the separated bond wafer is subjected to a reclaiming process (a refreshing process) including a surface treatment such as polishing and etching again. This process reduces or eliminates a step created at a non-bonding part, rough surface after the separation, and an effect of a layer of residual implanted ions, allowing repeated reuse of the wafer. Patent Document 2 for example suggests a reclaiming process of eliminating the effect of the implanted-ions layer remaining in a chamfered portion by the combination of chamfering and polishing.
Patent Document 3 discloses a reclaiming process performed on the separated wafer that includes polishing the surface of the wafer with a polishing stock removal of 2 μm or more, and repeated reuse of the separated wafers as bond wafers. Patent Document 4 discloses that when the separated wafer is repeatedly reused, about 5 μm of polishing is repeated 10 times at its maximum. Patent Document 5 discloses the polishing stock removal of the surface of the separated wafer ranges from 1 to 5 μm or is more than that, and a reclaiming process on the separated wafer is repeated several times.